Segmented stators for use in electromagnetic machines, such as hermetic compressor motors of a refrigeration system, are known in the art. The segmented stator assemblies typically include a plurality of segments that form the stator of the motor. The stator is typically contained within a shell, and a rotor and shaft are positioned for rotation within a bore of the stator. Each segment of the stator includes a yoke portion and a tooth portion. As is known in the art of electromagnetic machines, such as induction motors, brushless permanent magnet (BPM) motors, and switched reluctance (SR) motors, the stator teeth are wound with magnet wires to form winding coils having a plurality of phases.
End caps fit on the ends of segments of a stator to facilitate the placement of wire on the segments. For example, U.S. Pat. No. 6,584,813 to Peachee et al. and entitled “Washing machine including a segmented stator switched reluctance motor,” which is incorporated herein by reference in its entirety, discloses a segmented stator assembly that uses end caps on the segments. In addition, U.S. Pat. No. 2,688,103 to Sheldon; U.S. Pat. No. 2,894,157 to Morrill; U.S. Pat. No. 6,127,753 to Yamazaki; U.S. Pat. No. 6,509,665 to Nishiyama et al and U.S. Patent Application No. 2002/0084716 to Harter et al. disclose various examples of end caps for stators. The prior art end caps are typically glued to the segments, and winding coils are wound about the tooth portions of each segment and on portions of the end caps. Therefore, any problems with the end caps can produce poor winding characteristics in the winding coils, such as undesirable overlap of the winding coils or inefficient density of the winding coils about the tooth portions.
Segmented stators require various manufacturing steps to interconnect all the individually wound coils on the segments to form the phase windings. To interconnect the winding coils of the stator, it is known in the art to use a printed circuit board to interconnect the various winding coils of the stator. The printed circuit board is generally circular and has a plurality of terminal pads that connect to terminal pins on each end cap of the stator.
Rather than using a printed circuit board, interconnect wires can be used to connect the various winding coils of opposing electrical phases (voltages). Ends of the interconnect wires can be welded or soldered to terminal pins on the end caps of the stator, such as disclosed in U.S. Pat. No. 2,688,103 to Sheldon. The interconnect wire can be routed on the stator in several different ways. In one example, the interconnect wires can be routed around the outside portions of the segments. It is known in the art to provide hooks on the outboard side of a stator for routing the wires to route interconnect wires on the outside portion of the stator. In a compressor motor, however, routing wires on the outside portion of the stator is not desirable.
In another example, the interconnect wires can be routed within the inside portion of the stator. It is known in the art to use a stitcher ring to guide the wires to route interconnect wires on the inside portion of the stator. For example, a stitcher ring, having part no. 280138 and manufactured by Emerson Electric Co, is used in motors to route interconnect wires. The stitcher ring is a disc with a central opening for passage of a rotor shaft. The stitcher ring positions on a lead-end of the stator and fits partially over the bore of the stator. A plurality of hooks are provided on one side of the stitcher ring and are used to route wire between winding coils. In another example, U.S. Pat. No. 5,900,687 to Kondo et al. discloses an end plate having grooves for arranging the conducting wires between the coils of the various phases. The end plate is fixed onto an upper portion of the winding coils of the stator in the area of the bore.
Because the interconnect wires routed on a stator are positioned adjacent one another, a large voltage differential between the adjacent interconnect wires can produce phase-on-phase conditions in the motor and can cause premature failure of the insulation on the wires. In a compressor motor, any large voltage differential between adjacent wires can be magnified because the motor is used as a magnetization fixture where upwards of 1600 Volts and 1200 Amps may be passed through the stator at a given instant. In addition, a compressor motor can be used with a Pulse Width Modulated (PWM) drive. The waveform from the PWM drive may have high voltage spikes on the leading and trailing edges of the waveform, creating the need to separate the phase wires. Traditionally, motors use insulation made of MYLAR® or NOMEX® between the magnetic wires forming the separate winding coils. It is also known in the art to use secondary insulation between the interconnect wires interconnecting the winding coils. Unfortunately, such secondary insulation can increase the manufacturing costs and production time of the motor.
Some segmented stator assemblies use interlocking features or hinges on the segments to hold them together. For example, U.S. Pat. No. 6,127,753 to Yamazaki et al. discloses segments having hinged ends that connect adjacent segments together. Unlike the segmented stators having interlocking segments, some prior art segments for stators are not formed to directly interlock with other segments of the stator. Instead, such segments have ridged and slotted ends. The ends merely fit together on adjacent segments so that the segments are not physically held together in the absence of some other retaining structure. Hence, the stator segments are used to form a stator of the “loose” segmented type. “Loose” segmented stators typically require a secondary retention device, such as a heavy metal band, to hold the segments together when the segments are formed into the annular shape of the stator. The heavy band is positioned around the outside diameter of the segments to hold them together when manufacturing the motor or when transporting the stator as a separate part to customers. In addition, conventional segmented stators do not provide a ready way to axially align the segments to prevent unacceptable differences in tolerances during manufacture. Currently, no form of axial alignment for “loose” segmented stators is thought to exist in the art.
As noted above, segmented stators can be used in hermetic motors for a compressor of a refrigeration system. The compressor has an oil pump on the bottom of the compressor, which is known as the oil sump. Typically, oil is pumped up through a shaft of the hermetic motor, past the stator and rotor, and to the main bearing of the compressor. From the bearing, the oil is let loose on a lead end of the motor to drain back to the oil sump. The contours of the motor, such as the contours of the segmented stator, can determine how the oil is allowed to return to the oil sump from the lead end of the motor. In addition, oil from the oil sump in the hermetic motor can also pool in cavities and recesses of typical end caps, which can prevent the return of oil to the oil sump. If the motor does not have sufficient drain area, for example, the oil will become dammed on the lead-end of the motor. The damming of oil can cause higher oil circulation in the refrigeration system, can starve the oil pump of oil, and can hinder the performance of the compressor. On the other hand, if the motor has too much drain area for the return of the oil, then the stator may have less back iron than desired. A stator with less back iron can have higher magnetic flux saturation and reduced performance.
Typical stators for hermetic motors in compressors have flat areas defined on the outside diameter of the stator. The flat areas of the stator provide a drain area for the oil to pass from the lead-end of the motor to the oil sump. In some stators, the flat areas are made very large so that the material used to form the stator can be used efficiently. However, the large size of these flat areas in the stator can deform the shell of the motor. For example, the progression of the laminations forming the stator with the flat areas can create issues with shell deformation. In addition, the scroll shear pattern when used in a compressor can create issues with shell deformation because of the physical size of the flat areas on the outside of the stator. Thus, a trade off is typically made between the size of the flat areas in the stator and the efficient use of material used to make the stator.
The subject matter of the present disclosure is directed to overcoming, or at least reducing the effects of, one or more of the problems set forth above.